Epigenetic changes mediated by polycomb repressive complex 2 are associated with cisplatin acquired resistance in testicular germ cell tumor

Testicular germ cell tumors (TGCTs) represent the most common carcinoma affecting young men. TGCTs serve as a paradigm of chemo-sensitive tumors as more than 80% of metastatic disease can be cured with cisplatin-based chemotherapy. However, therapy resistance can occur, which results in poor patient outcomes. The mechanisms of cisplatin resistant in these tumors remain largely undefined. To study the mechanism of cisplatin acquired resistance we generated several independent, acquired resistant clones of parental NT2/D1, 833K and 2102EP testicular cancer cells employing an in vitro protocol designed to mimic the standard-of-care cisplatin regimen used to treat TGCT patients. We further characterized 10 of these clonal lines and confirmed stable cisplatin resistance ranging from 5- to 30-fold. After confirming the cisplatin resistance, we performed RNA seq transcriptomic profiling, differential gene expression analysis, DAVID and GSEA. Remarkably, RNA-seq based transcriptional profiling revealed highly significant alterations shared between the majority of the resistant cells regardless of their parental cell of origin. This includes apparent amplification of chromosomal region 17q21-25 in 8 of 10 lines. Unexpectedly, 7 of 10 lines had a highly significant enrichment of genes regulated by H3K27 methylation and polycomb repressive complex 2 (PRC2). Transcription factor prediction analysis of genes differentially expressed between resistant and parental cells revealed that polycomb complex members were among the most highly ranked predicted transcription factors responsible for the gene expression changes. These include EZH2, SUZ12, JARID2 and BMI1. We will present our ongoing studies investigating the role of PRC2 and H3K27 methylation in mediating cisplatin resistance in these cells and in patient samples. Together our data suggests that repression of H3K27 methylation may be a mechanism of cisplatin acquired resistance in TGCTs and that restoration of PRC2 function could be a viable approach to overcome treatment failure. Citation Format: Ratnakar Singh, Zeeshan Fazal, Emmanuel Bikorimana, Andrea Corbet, Jennifer Rodriguez, Alyssa Steege, Sarah J. Freemantle, Michael J. Spinella. Epigenetic changes mediated by polycomb repressive complex 2 are associated with cisplatin acquired resistance in testicular germ cell tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5188.